best way is to keep in your sight and close, even when well locked

when not possible, lock well (ulock and cable at a minimum) and be gone as little time as possible

know the neighborhood....some places you just should not leave bike un attended

remember organized bike thieves will also cut a frame and then part out....

good reason for an N+1 bike that is ugly or you would not miss for things like pub runs and use the good bike for the trails (N+1 is a good thing)